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From: Casey Schaufler <casey@schaufler-ca.com>
To: John Johansen <john.johansen@canonical.com>,
	casey.schaufler@intel.com, jmorris@namei.org,
	linux-security-module@vger.kernel.org, selinux@vger.kernel.org
Cc: linux-api@vger.kernel.org, linux-audit@redhat.com, sds@tycho.nsa.gov
Subject: Re: [PATCH v19 22/23] LSM: Add /proc attr entry for full LSM context
Date: Thu, 30 Jul 2020 13:44:29 -0700
Message-ID: <705fb82d-ad7a-2874-59ed-ba6bc7ae3722@schaufler-ca.com> (raw)
In-Reply-To: <e885d90d-c873-5ab4-235d-6171f49f4ee4@canonical.com>

On 7/30/2020 3:03 AM, John Johansen wrote:
> On 7/24/20 1:32 PM, Casey Schaufler wrote:
>> Add an entry /proc/.../attr/context which displays the full
>> process security "context" in compound format:
>>         lsm1\0value\0lsm2\0value\0...
>> This entry is not writable.
>>
>> A security module may decide that its policy does not allow
>> this information to be displayed. In this case none of the
>> information will be displayed.
>>
>> Reviewed-by: Kees Cook <keescook@chromium.org>
>> Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
>> Cc: linux-api@vger.kernel.org
>> ---
>>  Documentation/security/lsm.rst       | 28 +++++++++++
>>  fs/proc/base.c                       |  1 +
>>  include/linux/lsm_hooks.h            |  6 +++
>>  security/apparmor/include/procattr.h |  2 +-
>>  security/apparmor/lsm.c              |  8 +++-
>>  security/apparmor/procattr.c         | 22 +++++----
>>  security/security.c                  | 70 ++++++++++++++++++++++++++++
>>  security/selinux/hooks.c             |  2 +-
>>  security/smack/smack_lsm.c           |  2 +-
>>  9 files changed, 126 insertions(+), 15 deletions(-)

<snip>

>>  
>>  /**
>> diff --git a/security/security.c b/security/security.c
>> index d35e578fa45b..bce6be720401 100644
>> --- a/security/security.c
>> +++ b/security/security.c
>> @@ -754,6 +754,48 @@ static void __init lsm_early_task(struct task_struct *task)
>>  		panic("%s: Early task alloc failed.\n", __func__);
>>  }
>>  
>> +/**
>> + * append_ctx - append a lsm/context pair to a compound context
>> + * @ctx: the existing compound context
>> + * @ctxlen: size of the old context, including terminating nul byte
>> + * @lsm: new lsm name, nul terminated
>> + * @new: new context, possibly nul terminated
>> + * @newlen: maximum size of @new
>> + *
>> + * replace @ctx with a new compound context, appending @newlsm and @new
>> + * to @ctx. On exit the new data replaces the old, which is freed.
>> + * @ctxlen is set to the new size, which includes a trailing nul byte.
>> + *
>> + * Returns 0 on success, -ENOMEM if no memory is available.
>> + */
>> +static int append_ctx(char **ctx, int *ctxlen, const char *lsm, char *new,
>> +		      int newlen)
>> +{
>> +	char *final;
>> +	size_t llen;
>> +
>> +	llen = strlen(lsm) + 1;
>> +	/*
>> +	 * A security module may or may not provide a trailing nul on
>> +	 * when returning a security context. There is no definition
>> +	 * of which it should be, and there are modules that do it
>> +	 * each way.
>> +	 */
>> +	newlen = strnlen(new, newlen) + 1;
>> +
>> +	final = kzalloc(*ctxlen + llen + newlen, GFP_KERNEL);
>> +	if (final == NULL)
>> +		return -ENOMEM;
>> +	if (*ctxlen)
>> +		memcpy(final, *ctx, *ctxlen);
>> +	memcpy(final + *ctxlen, lsm, llen);
>> +	memcpy(final + *ctxlen + llen, new, newlen);
> if @new doesn't have a newline appended at its end this will read 1 byte
> passed the end of the @new buffer. Nor will the result have a trailing
> \0 as expected unless we get lucky.

@new will never have a newline at the end. The trailing nul comes
from the allocation being done with kzalloc(). This function has to
be considered in the context of its caller.

>
>
>> +	kfree(*ctx);
>> +	*ctx = final;
>> +	*ctxlen = *ctxlen + llen + newlen;
>> +	return 0;
>> +}
>> +
>>  /*
>>   * The default value of the LSM hook is defined in linux/lsm_hook_defs.h and
>>   * can be accessed with:
>> @@ -2124,6 +2166,10 @@ int security_getprocattr(struct task_struct *p, const char *lsm, char *name,
>>  				char **value)
>>  {
>>  	struct security_hook_list *hp;
>> +	char *final = NULL;
>> +	char *cp;
>> +	int rc = 0;
>> +	int finallen = 0;
> these are only used by context so they could be moved under its if, this
> is really just a style comment and I'll leave it up to you

Old coding habits die hard. Unless there's value to gain, I'll leave it
as is.

>
>>  	int display = lsm_task_display(current);
>>  	int slot = 0;
>>  
>> @@ -2151,6 +2197,30 @@ int security_getprocattr(struct task_struct *p, const char *lsm, char *name,
>>  		return -ENOMEM;
>>  	}
>>  
>> +	if (!strcmp(name, "context")) {
>> +		hlist_for_each_entry(hp, &security_hook_heads.getprocattr,
>> +				     list) {
>> +			rc = hp->hook.getprocattr(p, "context", &cp);
>> +			if (rc == -EINVAL)
>> +				continue;
>> +			if (rc < 0) {
>> +				kfree(final);
>> +				return rc;
>> +			}
>> +			rc = append_ctx(&final, &finallen, hp->lsmid->lsm,
>> +					cp, rc);
>> +			kfree(cp);
>> +			if (rc < 0) {
>> +				kfree(final);
>> +				return rc;
>> +			}
>> +		}
>> +		if (final == NULL)
>> +			return -EINVAL;
>> +		*value = final;
>> +		return finallen;
>> +	}
>> +
>>  	hlist_for_each_entry(hp, &security_hook_heads.getprocattr, list) {
>>  		if (lsm != NULL && strcmp(lsm, hp->lsmid->lsm))
>>  			continue;
>> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
>> index c13c207c5da1..43d5c09b9a9e 100644
>> --- a/security/selinux/hooks.c
>> +++ b/security/selinux/hooks.c
>> @@ -6288,7 +6288,7 @@ static int selinux_getprocattr(struct task_struct *p,
>>  			goto bad;
>>  	}
>>  
>> -	if (!strcmp(name, "current"))
>> +	if (!strcmp(name, "current") || !strcmp(name, "context"))
>>  		sid = __tsec->sid;
>>  	else if (!strcmp(name, "prev"))
>>  		sid = __tsec->osid;
>> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
>> index 6f0cdb40addc..d7bb6442f192 100644
>> --- a/security/smack/smack_lsm.c
>> +++ b/security/smack/smack_lsm.c
>> @@ -3463,7 +3463,7 @@ static int smack_getprocattr(struct task_struct *p, char *name, char **value)
>>  	char *cp;
>>  	int slen;
>>  
>> -	if (strcmp(name, "current") != 0)
>> +	if (strcmp(name, "current") != 0 && strcmp(name, "context") != 0)
>>  		return -EINVAL;
>>  
>>  	cp = kstrdup(skp->smk_known, GFP_KERNEL);
>>

--
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  reply index

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20200724203226.16374-1-casey.ref@schaufler-ca.com>
2020-07-24 20:32 ` [PATCH v19 00/23] LSM: Module stacking for AppArmor Casey Schaufler
2020-07-24 20:32   ` [PATCH v19 01/23] LSM: Infrastructure management of the sock security Casey Schaufler
2020-07-24 20:32   ` [PATCH v19 02/23] LSM: Create and manage the lsmblob data structure Casey Schaufler
2020-07-27 16:12     ` Stephen Smalley
2020-07-27 21:04       ` Casey Schaufler
2020-07-28 19:50     ` John Johansen
2020-07-24 20:32   ` [PATCH v19 03/23] LSM: Use lsmblob in security_audit_rule_match Casey Schaufler
2020-07-24 20:32   ` [PATCH v19 04/23] LSM: Use lsmblob in security_kernel_act_as Casey Schaufler
2020-07-28 10:34     ` John Johansen
2020-07-24 20:32   ` [PATCH v19 05/23] net: Prepare UDS for security module stacking Casey Schaufler
2020-07-28 10:57     ` John Johansen
2020-07-24 20:32   ` [PATCH v19 06/23] LSM: Use lsmblob in security_secctx_to_secid Casey Schaufler
2020-07-28 11:11     ` John Johansen
2020-07-28 23:41       ` Casey Schaufler
2020-07-29  0:30         ` John Johansen
2020-07-24 20:32   ` [PATCH v19 07/23] LSM: Use lsmblob in security_secid_to_secctx Casey Schaufler
2020-07-24 20:32   ` [PATCH v19 08/23] LSM: Use lsmblob in security_ipc_getsecid Casey Schaufler
2020-07-24 20:32   ` [PATCH v19 09/23] LSM: Use lsmblob in security_task_getsecid Casey Schaufler
2020-07-24 20:32   ` [PATCH v19 10/23] LSM: Use lsmblob in security_inode_getsecid Casey Schaufler
2020-07-24 20:32   ` [PATCH v19 11/23] LSM: Use lsmblob in security_cred_getsecid Casey Schaufler
2020-07-24 20:32   ` [PATCH v19 12/23] IMA: Change internal interfaces to use lsmblobs Casey Schaufler
2020-07-24 20:32   ` [PATCH v19 13/23] LSM: Specify which LSM to display Casey Schaufler
2020-07-27 20:36     ` James Morris
2020-07-27 20:40       ` John Johansen
2020-07-28 18:29     ` John Johansen
2020-07-24 20:32   ` [PATCH v19 14/23] LSM: Ensure the correct LSM context releaser Casey Schaufler
2020-07-24 20:32   ` [PATCH v19 15/23] LSM: Use lsmcontext in security_secid_to_secctx Casey Schaufler
2020-07-28 20:13     ` John Johansen
2020-07-24 20:32   ` [PATCH v19 16/23] LSM: Use lsmcontext in security_inode_getsecctx Casey Schaufler
2020-07-28 20:28     ` John Johansen
2020-07-24 20:32   ` [PATCH v19 17/23] LSM: security_secid_to_secctx in netlink netfilter Casey Schaufler
2020-07-27 20:37     ` James Morris
2020-07-24 20:32   ` [PATCH v19 18/23] NET: Store LSM netlabel data in a lsmblob Casey Schaufler
2020-07-24 20:32   ` [PATCH v19 19/23] LSM: Verify LSM display sanity in binder Casey Schaufler
2020-07-30  8:40     ` John Johansen
2020-07-24 20:32   ` [PATCH v19 20/23] Audit: Add new record for multiple process LSM attributes Casey Schaufler
2020-07-27 19:04     ` Stephen Smalley
2020-07-24 20:32   ` [PATCH v19 21/23] Audit: Add a new record for multiple object " Casey Schaufler
2020-07-27 20:40     ` James Morris
2020-07-24 20:32   ` [PATCH v19 22/23] LSM: Add /proc attr entry for full LSM context Casey Schaufler
2020-07-30 10:03     ` John Johansen
2020-07-30 20:44       ` Casey Schaufler [this message]
2020-07-30 20:57         ` John Johansen
2020-07-30 22:22           ` Casey Schaufler
2020-07-24 20:32   ` [PATCH v19 23/23] AppArmor: Remove the exclusive flag Casey Schaufler
2020-07-30  9:23     ` John Johansen

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